1. Field of the Invention
The present invention relates to a method and apparatus for testing a tunnel magnetoresistive effect (TMR) element such as a TMR read head element using the tunnel magnetoresistive effect or a magnetoresistive random access memory (MRAM) cell, to a manufacturing method of a TMR element, and to a TMR element.
2. Description of the Related Art
An evaluation test of a thin-film magnetic head with a TMR read head element is in general performed for determining whether or not the thin-film magnetic head is a non-defective product, during or after manufacturing the magnetic head. This evaluation test includes a reliability test for confirming that a breakdown voltage of the TMR head element is sufficiently high to withstand an extended period of use.
U.S. Pat. No. 6,473,257 discloses a testing method for confirming a reliability of a TMR read head element without damaging or breaking the TMR read head element. In this testing method, a performance of the TMR read head element such as its electromagnetic conversion performance is measured by using a test current with a predetermined current value. The test current value is determined by measuring a resistance of the TMR read head element when a predetermined initial current is flowing there through, or determined by repeatedly measuring a modified current when a reference voltage is applied to the TMR read head element and by measuring a resistance of the TMR read head element when the finally measured modified current is flowing there through.
However, this testing method disclosed in U.S. Pat. No. 6,473,257 requires a performance test of the TMR read head element such as an electromagnetic conversion performance test of the TMR read head element, and thus requires a great deal of expense in manpower and in time for confirming a reliability.
In order to solve such disadvantages in the prior art testing method, the inventors of this application have proposed, in U.S. patent Ser. No. 11/130,258, filed on May 17, 2005 a testing method of a TMR element. In the proposed method, constant currents with different current values are fed through the TMR element, an output voltage of the TMR element is measured for each current, a resistance of the TMR element is calculated for each current, and then the ratio of change in the resistances dMRR(%) is calculated.
According to this testing method proposed, reliability of the TMR elements can be easily confirmed in a short period of time. However, because the ratio of change in the resistances dMRR(%) has extremely strong correlation to the resistance of the TMR element and also there are mixed influences of film area and film material, it is difficult to clearly judge whether the TMR element is good product or not with reliability.